fix: handle settings with missing shared section

This allows configuration files without a `shared` field, using the
default value if missing.

Before:

    $ pueued -vv -c /dev/null
    Error: Error while reading configuration.

    Caused by:
        Error while reading configuration:
        missing field `shared`

After:

    $ pueued -vv -c /dev/null
    21:12:26 [INFO] Restoring state
    21:12:26 [INFO] Using unix socket at: "/run/user/1000/pueue_rycee.socket"

CHANGELOG.md

@@ -16,6 +16,8 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 
 - Include priority in `Task`s' `Debug` output
 
+- Fix reading of configuration files that lacks a `shared` section.
+
 ## [3.3.3] - 2024-01-04
 
 ### Fixed

pueue_lib/src/settings.rs

@@ -194,6 +194,7 @@ pub struct Settings {
     pub client: Client,
     #[serde(default = "Default::default")]
     pub daemon: Daemon,
+    #[serde(default = "Default::default")]
     pub shared: Shared,
     #[serde(default = "HashMap::new")]
     pub profiles: HashMap<String, NestedSettings>,